mcguirjf

Do you wait for your Gages to read zero before starting, or do you go right to start?

I noticed if I just go to start from off the engine will only crank 1-2 seconds before coming to life. If I wait for Gages to go to zero, it may take an additional 2 seconds.

Thoughts? I know my fuel pressure goes right to zero after the fuel pump primes. I don't believe the C4 L98's have a fuel pressure check valve.

My fuel pressure when running and at prime is about 40 psi.

New reman injectors from FIC.

New Delphi fuel pump assembly installed.

RICHARD TILL

How do you know for certain that the fuel pressure goes to 0 after the fuel pump primes??

eschoendorff

I turn the key until the motor makes motor noises.

DMITTZ

When starting I usually until I hear the fuel pump has pressurized the fuel system then start (about the time the gauges zero), otherwise on my car it takes longer to start if it try to crank I right away.

When I turn the key part way I can hear a little hum for about 1-2 seconds which is the fuel pump pressurizing the fuel system, once the hum stops (gauges zero) then I start the motor.

I have an adjustable fuel pressure regulator with a gauge and on my car once the key is turn part way and the fuel pump pressurizes the system, it stays at full pressure and does not drop back to zero. In fact I have noticed that even after turning the engine off the fuel pressure stays at full pressure for a few minutes before gradually going lower until it reaches Zero maybe 20-30min after the car is shut off.

I run my fuel pressure at around 45psi but I think stock motor should be about 42psi. It seems odd that your fuel pressure temporarily goes to zero after the fuel pump has pressurized the system... do you have a fuel pressure gauge on it or how did you know it is temporarily going to zero?

PatternDayTrader

I think it sounds fine to me. It makes perfect sense that it would take slightly longer to fire up if you first allow the fuel pressure to return to zero before engaging the starter.

DMITTZ

As I stated my car has an aftermarket adjustable fuel pressure regulator so it may function differently. But when the fuel pump primes in my car that pressurizes the system and it stays pressurized until the motor is started, do the stock fuel pressure regulators not allow the pump to pressurize the fuel system before starting as mine does? I thought they would to allow easier starting, rather than waiting until the motor is cranked to build fuel pressure...or forcing the driver to crank the motor before the fuel pump finishes priming the system...

most cars I have owned including my corvette started better once the fuel pump had primed/pressurized the system rather than cranking before it had completed priming...

just trying to determine why the OP's fuel pressure goes to zero after the pump primes the system, by the time the gauges Zero (a few seconds)...seems odd to me but my car is not stock so it my function differently than a stock vehicle...

mcguirjf

I just checked under the hood and the return line has a inline diaphragm. Is this suppose to hold pressure? The fuel pressure regulator is located between the two fuel rails which Would lead me to believe that the diaphragm is what holds pressure.

The schrader valve is located on the passenger side fuel rail.

I have read on later C5+ that pressure is held for long time and bleeds down slowly, but I believe they have a check valve at the fuel pump assembly.

Do I need to replace the return fuel line with the diaphragm?

mcguirjf

Here is picture of the diaphragm in question.



Located just under the bracket.

Another picture with it located just under AC hose. Of course.

Nowhere Man

I start it like any other modern engine. Hit the key until it runs.

mcguirjf

I found a couple additional threads with no results. Screw it! Nowhere man, you got the logic in this one.

Patsgarage

If the car has been sitting for some time I cycle the ignition a few times before starting, otherwise I just crank it over. Starts after 1-2 seconds everytime. (Hope I didn't jinx myself)

cv67

x2 turn the key and start
If youre lloosing all pressure you have a problem somewhere
Pressure regulator should be inline towards the rear of the plenum area if I remember correctly pull the vacuum line off see if its wet for starters

Tom400CFI

That is not right. It shouldn't do that (go to zero). L98's do have a check valve in the fuel pump.



And, to answer your question earlier about the diaphragm in your "return line", that doesn't "hold pressure", the regulator does -or should. That thing is your pic, is I BELIEVE, a device for absorbing/smoothing fuel pressure pulses, and I also believe that is your feed line, not your return.

If you're losing pressure immediately after pump shuts off, you need to pinch off your rubber feed and return, see if it drops. Only places it can leak are injectors and regulator.

If no drop, pinch off return, test again; if it drops, it's your check valve in the pump.

If no drop, pinch feed line, test again. If it drops, it is your regulator.

JrRifleCoach

DMITTZ

As I noted earlier I replaced my stock fuel pressure regulator many years ago with an adjustable one, so my car may function differently than stock.

However, my car does hold pressure once the fuel pump primes, and only gradually bleeds off that pressure over 20-30min if the cars not running. I suspect that when stock it would have functioned the same way, and it seems logical to me that the fuel system should hold pressure once the pump primes and not let it immediately drop back to 0.

The suggestions Tom400CFI gave seems like a good place to start.

let us know what you find.

having said that if the only problem you are having is that it takes a few seconds of cranking to start the car, its up to you whether or not you want to spend the time try to figure out what is only a very small issue at this point.

maddogwyatt

THE 383 admiral

non OE. I have a High performance external fuel pump. NO check ball. this is not needed! I need to start immediately. Pressure does not Hold in my rails. When the pump is off.

Frodo

According to my GM service manual, for 1989 Corvette, there are 4 reasons for fuel pressure to drop.
1. In-tank fuel pump check valve not holding.
2. Pump coupling hose or pulsator leaking.
3. Fuel pressure regulator valve leaking.
4. Injector(s) sticking open.

Not mentioned in this section but mentioned earlier in the manual is any connection in the fuel supply line, such a damage or loose fittings or any damage to the fuel line from the tank to the engine bay. Also mentioned are the fuel pressures acceptable, 34 to 47 psi.
My own 1989 C4 will hold pressure for over an hour, measured at the fuel pressure test connector. I have an aftermarket adjustable fuel pressure regulator, however stock regulator should also hold pressure after shut down.
I hope this information will aid in finding your problem.

mcguirjf

Amazon order placed for new AC Delco fuel pressure regulator. Will post the results.

canuck buick

So what were the results?